Ferro alloy containing aluminum and manganese

ABSTRACT

THE IHHERENT INSTABILITY IN AIR OF AN ALLOY CONSISTING MOSTLY OF MANGANESE AND ALUMINUM, THE MN:AL RATIO BEING WITHIN THE RANGE 1.5 TO 0.67, THE ALLOY CONTAINING A FEW TENTHS PERCENT OF CARBON, IS COUNTERACTED BY THE ADDITION THERETO OF A SMALL AMOUNT OF TITANIUM OR ZIRCONIUM.

United States Patent ffi ce FERRO ALLOY CONTAINING ALUMINUlVI AND MANGANESE William W. Gullett, College Park, Md., assignor to Diamond Shamrock Corporation, Cleveland, Ohio No Drawing. Filed Jan. 8, 1971, Ser. No. 105,088 Int. Cl. C22c 21/00 U.S. Cl. 75-134 M 7 Claims ABSTRACT OF THE DISCLOSURE The inherent instability in air of an alloy consisting mostly of manganese and aluminum, the MnzAl ratio being within the range 1.5 to 0.67, the alloy containing a few tenths percent of carbon, is counteracted by the addition thereto of a small amount of titanium or zirconium.

BACKGROUND OF THE INVENTION This invention relates to the art of steel making and more particularly to the de-oxidation of molten steels. The invention is particularly concerned with improving a ferro alloy containing aluminum and manganese for use as a de-oxidizing agent in the production of steels. By the expression ferro alloy, as used herein, is meant an alloy used in the production of steel: it may or may not of itself contain iron.

It is known to add manganese to molten steel whereby to remove oxygen therefrom, to neutralize the elfect of sulfur and to render the steel free from red shortness. Conventionally, it had been the practice to add the manganese in the form of standard ferro-manganese. However standard ferro-manganese normally contains a considerable amount (several percent) of carbon, and hence use of term-manganese for manufacturing low-carbon steels is out of the question.

As is disclosed in, for example, U.S. Pat. 501,233, Richards and Hunt, it heretofore was known to enlarge the field of usefulness of ferro-manganese in the production of steels by adding thereto aluminum, whereby to make an alloy containing aluminum and manganese together with iron. It was known that the addition of aluminum brought about a marked reduction in the carbon content of ferro-manganese, and hence made it possible to use this material in the production of steels intended to have low, or very low, contents of carbon.

It was also known amongst steel metallurgists to use aluminum and certain alloys of aluminum for the same general purpose as that of the above-described aluminumcontaining ferro-manganese. This practice was described in, for example, U.S. Pat. 2,767,084 to Chandler, and in particular in lines 20-37 of column 1 of said patent. It is there pointed out that both aluminum and silicon are capable of tie-oxidizing steel, and that manganese can be used in conjunction with aluminum for the purpose of de-oxidizing molten steel and to the production of socalled killed or semi-killed steels.

Out of these prior investigations it became evident that a manganese-aluminum alloy in which manganese amounted to about half or somewhat more than half of the composition should be a desirable tool in manufacturing steels. The several desirable characteristics of Mn-Al alloys containing 50 percent or more of manganese include: a pronounced activity as a de-oxidizer; a desirably low melting point; ready solubility in molten steel; and particularly a desirably high density which ensures its sinking into the melt of steel. U.S. Pat. 3,119,688, Rodgers et al., is directed to the concept of de -oxidizing molten steel with manganese-aluminum alloys in which 3,684,494 Patented Aug. 15, 1972 the manganese varies between 50 and 75 percent and the aluminum content varies between 50 and 25 percent.

On the basis of experience with alloys prepared from ferro-manganese and aluminum, in which alloys at least 50 weight percent but not more than 75 weight percent of the sum of the manganese and the aluminum consists of manganese, it was predicted that such an alloy containing about 60-40 percent of one of the components and about 40-60 percent of the other component would be an outstandingly advantageous de-oxidizing agent in the production of steel. However, when alloys within this predicted composition range and containing a few tenths percent carbon were actually prepared from ferro-manganese and aluminum, it was discovered that they are inherently unstable. By unstable I here mean that the freshly cast and cooled ingot spontaneously decrepitates or crumbles to powder after a period of exposure in air varying between several weeks and a few days depending mainly on the amount and character of its impurities. This phenomenon is thought to be surprising in the light of the fact that other Mn-Al alloys of substantially different ranges, e.g., -30 or 30-70 percent, are fully stable in air. By reason of this phenomenon-which may or may not have a satisfactory scientific explanation-the veryjheart of the full range of Mn-Al alloys has heretofore been'unavailable for use, in any practical sense. When the Mn-Al alloy decrepitates, it is still essentially a Mn-Al alloy of the same analysis (with less carbon content and slightly higher oxygen content) but it is now in the form of a very fine powder generally less than 20 mesh.

The standard practice for making ferroalloy additions to steel is to drop the alloy into the molten steel from a height sufficient for the alloy to penetrate the slag layer on top of the steel and enter the molten steel. This is particularly true of ferroalloys that are lighter or have less density than steel itself. If the ferroalloy floats on top of the slag layer, it may burn up or react with the slag. In the case of aluminum which has a density close to steel slags, it is not uncommon for the aluminum to burn up. If the aluminum sinks only into the slag layer, it may react with the silica in the slag to form silicon metal which in turn may introduce harmful silicon metal into the steel instead of the steel being de-oxidized with aluminum intended. It is obvious that a decrepitated Mn-Al alloy in the form of a fine powder would make a very poor addition agent to steel because it would tend to float on the slag or lay on the slag due to surface tension and subsequently burn up.

It is to be noted, in the above character, that if at 60-40 percent, or 50-50 percent, a Mn-Al alloy be prepared using a very highly purified manganese such as electrolytic manganese, one does not experience the aforesaid instability. From the fact that aluminum-including both primary and secondary aluminum-contains almost no carbon, and from the fact that electrolytic manganese has substantially no carbon, it is conjectured that the aforesaid instability phenomenon is related to some role of carbon in ferro-manganese from which the Mn-Al alloy has been prepared.

In this connection, it should be remarked that Tat. 501,233, in the second column thereof, teaches that by adding aluminum to ferro-manganese one can materially reduce its carbon content. While this is true to a limited extent, it is a fact that by addition of aluminum to ferromanganese containing the usual concentration of carbon, one cannot depress the carbon content of the resulting alloy below about 1.0 percent. This residual amount of carbon in the resulting manganese-aluminum alloy renders the alloy ineffectual as a tool in de-oxidizing molten steel.

A process for preparing an alloy from ferromanganese and aluminum comprises melting aluminum and introducing ferro-manganese into the aluminum melt beneath the surface of the molten aluminum. Any one of the following commercial grades of ferro-manganese can be utilized in said process.

(a) standard grade-containing 6.0 percent C, more or less,

(b) medium carbon ferro-manganese-containing 0.5-

1.5 percent C.,

(c) low carbon ferro-manganese--containing not more than 0.5 and down to 0.05 percent carbon.

When Mn-Al alloys in the range above noted are prepared from ferro-manganese of any one of the above types, the carbonaceous content of the ingot, upon cooling the ingot, tends to precipitate out at the grain boundarms.

1 Upon exposure of the ingot to air containing normal amounts ofwater vapor, there are formed from the carbon content gaseous hydrocarbons and the ingot tends to decrepitate into individual-crystals. One can smell the hydro-carbonaceous gas when a mass of the aforesaid alloy decrepitates in a container exposed to air, the odor being similar to that of acetylene. In pointing to carbon as being the probable cause of the aforesaid instability of the 40450 alloys, one cannot entirely rule out the possible roles of phosphorous and arsenic found (in minute amounts) in the ferro-manganese.

STATEMENT OF THE INVENTICN DESCRIPTION OF THE PREFERRED EMBODIMENTS The aforesaid instability in air can be avoided by adding to such inherently unstable Mn-Al alloys containing carbon, a very small amount of Ti or Zr or mixtures thereof. Numerically the added amount of this improver may range between 0.05 and as much as 5.0 weight percent; the lower limit has been found to give a noticeable improvement, whilst the upper limit has been found to take care of very poor grades of term-manganese and constitute an upper limit beyond which additional improvement does not occur. The presence of small amounts of titanium, zirconium or mixtures thereof is believed to prevent segregation of carbonaceous components at the grain boundaries. Whatever the scientiticexplanation, it is a fact that by practicing this expedient, an otherwise inherently very unstable alloy is rendered satisfactorily stable without at the same time depreciatin'g any of its value as a de-oxidizing agent in the preparation of steel. When titanium is incorporated by itself the preferred range is from about 0.05 to about 3.0 percent. The preferred range of zirconium when added individually is from about 0.05 to about 5.0 percent. A preferred alloy effective as a de-oxidizing agent for steel melts and stable in air comprises in percent by weight of the alloy composition from about 40 to 60 percent of manganese, from about 2.0 to about 10.0 percent of iron, from about 0.04 to about 0.80 percent of carbon, from about 0.05 to about 5.0 weight percent of a metal selected from the group consisting of titanium, zirconium and mixtures thereof and balance aluminum.

The invention will now be further described with reference to the following specific examples:

EXAMPLE 1 In an induction furnace operating at a temperature of about 1400 F. 16 pounds of aluminum analyzing 99 percent Al, were melted and to the melt 24 pounds of form-manganese containing 0.40 percent carbon and 92 percent manganese, balance iron were slowly added. The temperature of the melt was increased as the ferro-manganese was added, to a final maximum temperature of about 2000 F. This operation took about ten minutes. Thereupon, the temperature of the melt was maintained at 2000 F. until all of the ferro-manganese had become dissolved. Then one pound of titanium metal in the form of small sticks was added to the melt, and the temperature of the melt increased to 2350 F. When the added titanium had dissolved in the melt, a small amount of dross was skimmed from the surface of the melt and the molten metal poured into cast-iron chill moulds yielding ingots having a thickness of about 2 inches. The castings were cooled in air. When cool the ingots were stored in containers exposed to air for several months, showing no decrepitation or other evidence of instability.

The product an especially preferred alloy of the instant invention, had the following approximate analysis:

Although titanium was added as such in the above example it may also be added in combination'as ferrotitanium, aluminum-titanium alloy and the like provided the specified quantity of titanium is contained in these materials.

EXAMPLE 2 An alloy was prepared by the same procedure followed in Example 1 with the exception that 4.5 pounds of aluminum analyzing 99 percent A1, 5.5 pounds of ferromanganese containing 0.27 percent and 92 percent manganese, balance iron and 3 ounces of zirconium sheet clippings were substituted respectively for the aluminum, ferro-manganese and titanium employed in Example 1.

The alloys of Examples 1 and 2 upon testing were each found to be effective as de-oxidizers of steel melts. They had full de-oxidizing properties and enjoyed the standard density feature which makes Mn-Al alloys so attractive for use as a tie-oxidizing tool. Continued storage in air did not result in decrepitation of these alloys.

Percent as included in this specification refers to percent by Weight of the alloy composition unless otherwise stated.

I claim:

1. In the process of making a manganese-aluminum alloy from commercial term-manganese, in which alloy the content of manganese is about 60-40 weight percent and the content of aluminum is about 40-60 weight percent, involving melting the aluminum and then dissolving ferro-manganese in the aluminum melt, the step of rendering the resulting alloy inherently stable in air which consists in incorporating a small amount of a stability-conferring agent in the aluminum-ferro-manganese melt, said stability-conferring agent being selected from the group of metals consisting of titanium, zirconium and mixtures thereof and being added in an amount of from 0.05 to 5.0 weight percent.

2; The process of claim 1 wherein the titanium is from about 0.05 to about 3.0 percent by Weight of the alloy.

3. The process of claim 1 wherein the zirconium is fromabout 0.05 to about 5.0 percent by weight of the alloy.

4. A tie-oxidizing agent for steel melts in the form of an alloy stable in air comprising (1) from about 40 to about 60 weight percent of manganese, (2) from about 2.0 to about 10.0 Weight percent of iron, (3) from about 0.04 to about 0.80 weight percent of carbon, (4) from about 0.05 to about 5.0 weight percent of a metal selected from the group consisting of titanium, zirconium and mixtures thereof and (5) balance aluminum.

5. A de-oxidizing agent for steel melts in the form of an alloy stable in air having the following approximate composition:

6. The de-oxidizing agent of claim 4 wherein the titanium is from about 0.05 to about 3.0 percent by weight 1 of the alloy.

6 7. The de-oxidizing agent of claim 4 wherein the zirconium is from about 0.05 to about 5.0 percent by weight of the alloy.

References Cited UNITED STATES PATENTS 2,436,001 2/1948 Gaines 75-134 M X 3,119,688 1/1964 Rodgers et a1. 75134 M X 3,239,362 3/1966 Brandstatter 7557 X 10 3,592,637 7/1971 Brown et a1 75138 L. DEWAYNE RUTLEDGE, Primary Examiner E. L. WEISE, Assistant Examiner U.S. Cl. X.R. 7557, 138 

